This invention relates to an electromagnetic induction coil or antenna device, and more particularly to such a coil device embedded in hearing aids for receiving sound signals generated by a primary electromagnetic induction coil or a loop coil which is laid down in a room.
The invention herein is principally described and illustrated in a specific embodiment wherein it is applied to personal hearing aids. Conventionally, since an electromagnetic induction coil (hereinafter referred to as an induction coil) built in personal hearing aids couples magnetically to a sound magnetic field which is generated in response to a sound signal current flowing through a primary induction coil laid down inside the floor of a room or placed in the ceiling thereof, it is very useful for a mass-hearing medium of persons who are hard of hearing in an educational field. Such a hearing medium is able to reduce obstacles in hearing due to the distance between speaker and listener and environmental noises, comparing it with the way of directly receiving sounds through a microphone. Accordingly, it greatly assists in an improvement of S-N ratio and, in particular, is effective in an educational field of persons who are hard of hearing. Recently, it has been popular to use, in a family, such a device in enjoying television. However, in the conventional induction coil devices, the induction coil is fixedly arranged to the body of the hearing aid with a constant positional relationship, and also the distribution of the intensity of the sound magnetic field at a hearing position is directional. For these reasons, there has been a great disadvantage in that when a person who uses a hearing aid changes his posture, the posture of the induction coil embedded in the hearing aid is resultantly changed and also the output signal of the ear-phone of the hearing aid varies remarkably. These difficulties have been drawbacks in the case of aiding the hearing ability of hearing loss children through music or physical exercise and in the case when persons enjoy a television with their bodies relaxed.
In order to solve such problems, various induction coil devices have been proposed, but these have suffered from a dead angle not so as to obtain sufficient advantages.